1. Field of the Invention
The present invention relates to rail car braking systems, and more particularly to a rail car load sensor configured for use with a rail car brake controller. The rail car load sensor adjusts the braking force applied by the rail car brake controller in accordance with the amount of load or weight in the rail car for optimally stopping or braking the rail car in the least amount of distance while eliminating wheel sliding.
2. Description of the Prior Art
Rail car braking systems generally include pneumatically operated brake cylinders, control valves for directing air to the brake cylinders, a main valve located in the train locomotive for controlling the operation of the control valves, and distribution piping connecting the brake cylinders and valves to an air source. An engineer operates the rail car brakes by activating the main valve, which causes a pressure drop in the distribution piping. This pressure drop signals the control valves to distribute air to the brake cylinders for braking the rail cars.
A serious problem with conventional rail car brake systems is wheel sliding caused by excessive braking force applied to an empty rail car. Due to the recent use of lightweight materials for rail cars, the empty weight of a rail car is significantly lighter than the loaded weight of the rail car. Thus, if the rail car brake system is designed to stop the rail car when it is loaded, it applies too much braking force to the rail car wheels when the rail car is empty, thus causing wheel sliding. Conversely, if the rail car brake system is designed to stop the rail car when it is empty, it will not provide sufficient braking force to stop the rail car when the rail car is loaded. Damaged wheels due to wheel sliding is the largest single maintenance cost for many rail car owners.
In response to these problems, one prior art solution involves the use of "loaded/empty" sensors coupled with the rail cars' suspension systems. A loaded/empty sensor operates on the principle that a loaded rail car will have a shorter distance from the car body to the unsprung portion of the rail car suspension than will an empty car.
Prior art loaded/empty sensors include a lever positioned on the springs of the rail car suspension and a lever-operated valve coupled with the rail car's brake cylinders. The lever moves when the rail car's springs compress or expand in response to changes in the amount of weight or load in the rail car. When the lever moves upwards a predetermined amount, it operates the valve, thus diverting some of the air intended for the brake cylinder into an air reservoir. This reduces the air pressure delivered to the brake cylinder, thus reducing the braking force of the brake system.
Although prior art loaded/empty sensors partially reduce wheel sliding, they suffer from several limitations that limit their effectiveness in many applications. For example, prior art loaded/empty sensors merely sense whether the car is completely loaded or completely empty, but do not sense intermediate ranges such as when the rail car is partially loaded or partially empty. Thus, these prior art loaded/empty sensors cannot accurately measure a full range of rail car weight and thus cannot optimally control the rail car brakes for both braking the rail car in the least amount of distance while also eliminating wheel sliding.
Another problem with prior art loaded/empty sensors is that they cannot be easily adjusted to compensate for changing brake system conditions such as system air pressure and temperature. Additionally, since prior art loaded/empty sensors utilize mechanical levers and switches, they are subject to wear, freezing, and contact failure.
Accordingly, there is a need for an improved rail car brake system that overcomes the limitations of the prior art. More particularly, there is a need for an improved rail car load sensor that optimally stops or brakes the rail car in the least amount of distance while eliminating wheel sliding.